Conventional 12-lead Electrocardiography
It is known that the use of electrocardiography for detecting electrophysiological changes in the heart is the simplest and the most effective non-invasive diagnostic method at present (See refs. 1 and 2). Hereafter, ECG would represent current conventional 12-lead electrocardiography. Electrocardiograms from ECG are effective in the diagnosis of MI of anterior-septal, anterior, inferior, and lateral ventricular walls. However, the sensitivity is about 50-70%. Furthermore, because it can not determine the size of infarction, many difficult and complicated cases can not be definitely diagnosed. In addition, because the quantity of information from the scattered 12-lead electrodes is smaller and non-uniform, false negative diagnosis are inevitable and the seriousness of a patient's condition can not be estimated from the size of pathological changes in ECG.
The theoretical foundation of the 12-lead ECG and its method of diagnosis is built upon the mono-equivalent dipole theory, in which the heart is considered as a small dipole at the center of an infinitely sized sphere of homogeneous conductor. During a cardiac cycle, countless dipoles generated by the electrocardiac changes are simplified into a series of instantaneous resultant vectors with respect to a fixed point. Due to the limited amount of information provided by the 12-lead ECG, this simplifying assumption is required for the construction of the electrophysiological model of the heart. However, this assumption is far from the actuality, because:
1) the human body is not spherical, PA1 2) the conductivity of different parts of human body tissue is nonhomogeneous, PA1 3) the heart is located at one side of the human body, and PA1 4) the relative volume of human body to the heart is not infinite. PA1 1) cardioelectric peak potentials are the most informative parameters in characterizing electrophysiological voltage changes of the heart; PA1 2) peak potential values of each cardioelectric wave components and their displacements measured on body surface form distinct contours which can be used for differentiation and diagnosis of heart diseases; PA1 3) EPM isopotential map provides a direct correlation between areas of electrical activities on the myocardial walls and areas of electrocardiographic signals on the body surface; PA1 4) EPM isochronous maps provide a direct measurement for the depolarization and repolarization condition of the heart; PA1 5) multiple-lead measurement of electrocardiac activities by EPM widens the information obtainable from conventional ECG and enables more specific anatomical diagnosis. PA1 1) reduce information overload by going from 10's or 100's of SIM contours to generally 5 or 6 EPM maps (in some cases, a finer resolution of more than 6 maps will be needed), while capturing most of the clinically significant SIM data; PA1 2) enhance signal to noise ratio in detecting pathological changes because of distinct, either positive or negative and diagnostic patterns: PA1 3) provide time parameters to indicate the speed and direction of heart excitation during cardiac depolarization and repolarization; PA1 4) provide direct correlation between areas of electrical activities originated from the myocardial walls and areas of electrocardiographic signals covered by the body surface leads; PA1 5) in conjunction with the EPM apparatus, simplify the application of leads and tuning and adjustment of electrode channels. PA1 1) detecting and organizing high quality electrocardiographic information over the body surface via a non-invasive method, PA1 2) building of simple but comprehensive peak isopotential, isochronous, and their combined maps from such data for easy recognition and analysis, PA1 3) deriving contour parametric values for quantitation. PA1 4) generate highly reliable and consistent data of electrophysiological changes in the heart, PA1 5) provide a simple, portable, low-cost, easy-to-use apparatus, PA1 6) achieve automatic diagnostic capability for heart PA1 7) provide fine detail information about the heart abnormalities, such as the size of MI, degree of conduction blocks in myocardial depolarization and repolarization, and PA1 8) provide conventional 12-lead ECG information - - -EPM can be used as a conventional ECG. PA1 1) identification of peaks, both positive and negative and any possible subpeaks (local maxima and minima when voltage is plotted against time), for each point, PA1 2) determination of voltage and time of each P, Q, R, S, +T, and -T (and r' and s' if present) wave peaks derived from (1) , PA1 3) construction of contour maps from description (2), in which the contours are either isopotential or isochronous lines, PA1 4) identification of maxima and minima of contours from (3), such as R-centers, Q-centers, multiple centers, etc., PA1 5) determination of gradient (slope) values of the region around the local maxima and minima (4), such as R-notches, etc., PA1 6) determination of the area covered by boundaries of contour peaks and valleys, as derived from the maxima and minima information (4), and PA1 7) deviation of values of (4)-(6) in patients from normal data constructed from group mean value .+-.2 standard deviation of corresponding maps, PA1 8) automatic diagnosis. PA1 1) an elastic waistcoat (thoracic corset) with embedded soft electrodes, PA1 2) Wilson unipolar limb lead system as voltage references, PA1 3) signal preprocessor including multiple body surface electrocardiographic channels and a Wilson circuit, PA1 4) multiplexer from the preprocessor (3) to the acquisition unit (5), PA1 5) high speed data acquisition unit composed of a main amplifier, an A/D converter, two data latches, random access memory, a RAM address counter, a data bus buffer, an address arbiter, an interrupt signal generator, an address decoder, a function and time-sequence controller, a control-word register, and a channel address latch, PA1 6) computer with the software to perform the EPM method, and PA1 7) display and printer to the computer.
Although many electrocardiographic phenomena can be explained by this theory, some electrocardiographic phenomena of ECG can not be explained. Thus the electrocardiography is unsatisfactory in clinical applications.